1. Field of the Invention
This invention relates to a direct method for the production of high-grade, high-purity ferromanganese, more particularly, to a direct method for production of ferromanganese having high Mn content and exceedingly low C and P content.
2. Description of the Prior Art
Demand has increased in recent years for high quality steel materials having superior qualities in terms of workability, durability, weatherability, resistance to particular atmospheres, etc. At the same time, there has arisen a need to produce such steel materials more economically. In line with these trends, higher quality has come to be demanded for Mn-containing ferroalloys for use as deoxidization agents and alloying additives in the production of steel. In certain applications, for example, there has arisen a need for ferromanganese having a composition wherein Mn.gtoreq.90%, Si.ltoreq.1.5%, C.ltoreq.0.1%, and P.ltoreq.0.05%.
Up to now, the need for such a high quality Mn source with low impurity content has been met by electrolytically produced metallic Mn or by medium- or low-carbon ferromanganeses. Electrolytic Mn, although satisfactory from the point of impurity content, is disadvantageous because of its high cost of production and because it exists in the form of thin flakes which, being light in weight, give a low yield in use. On the other hand, medium- and low-carbon ferromanganeses, although lower in price than electrolytic Mn, are disadvantageous in a number of points. They require the use of complex production methods, give low Mn yield in the course of production and result in a high unit electrical power cost. Moreover, as will be noted from the standards for Grade A low-carbon ferromanganeses (85-90% Mn, 0.1-0.7% C, not more than 2.0% Si, not more than 0.20% P and not more than 0.02% S), it is not easy to obtain carbon-containing manganese products which meet the quality requirements set forth above, especially in terms of C and P content.